Transform Effects Strip Real Values
This could be a solution with VSE, but you'll get a blurried image (if you scale 300%)

Some consideration first:

The effect strip will scale always from the center of the image.

If you want to scale from the point A (508x291px from the top-left corner), you have to move the point A to the center first, then scale.

Pan and zoom in VSE


Add the first effect stript to translate the image by the offset you need.
Add the second effet strip to scale (3 = 300%)


Some math:

If your image dimensions are 1920x1080px:

first effect strip (position)

center: xc=960, yc=540

pointA: xa=508, ya=291

translation: xc-xa, yc-ya = 960-508, 540-291 = 452, 249



second effect strip (scale)

scale 3 = 300%

As you can see, the quality of the image is very low.
Since you are scaling 3 times the size, the resolution is 3 times lower.



Note

When you deal with scale in VSE, you have to pay attention to the original size and the render size.

When you add an image (or a movie clip) in the video sequencer editor, the image will be scaled to the render size.

If you want the image to maintain the original size, you have to check the "Image offset" option (transform in pixel).



Doing so, you can pan the image and center the point of interest but you cannot scale it down, because the image will be cropped.

If you want to zoom an image, I suggest you to use the node compositor or a camera moving in front of an image plane in 3d View.

Pan and zoom in 3D View

Using the 3d View, the image texture can be bigger than the render size.


Activate the "import images as planes" add-on, if it is not yet activated





Import the image to stage





Some considerations about the options:


Check "Shadeless"
If you're importing image with alpha channel (png), check "Use Alpha" and "Z Transparency"
If you want the image to have precise dimensions, the best choice is "Plane dimensions: Dots/BU)": it allows you to determine the dimensions starting from the pixel size (eg: 1920 x 1080px at 100 Dots/BU -> plane dimensions: 1.920 x 1.080 BU)


Pan and zoom in Node Compositor

Here a possible node compositing: